The optimal approach to assess risk of venous thromboembolism in hospitalized medical patients is unknown. We examined how well the Caprini risk assessment model predicts venous thromboembolism in hospitalized medical patients.

Between January 2011 and March 2014, venous thromboembolism events and risk factors were collected from non-intensive care unit medical patients hospitalized in facilities across Michigan. After calculation of the Caprini score for each patient, mixed logistic spline regression was used to determine the predicted probabilities of 90-day venous thromboembolism by receipt of pharmacologic prophylaxis across the Caprini risk continuum.

A total of 670 (1.05%) of 63,548 eligible patients experienced a venous thromboembolism event within 90 days of hospital admission. The mean Caprini risk score was 4.94 (range, 0-28). Predictive modeling revealed a consistent linear increase in venous thromboembolism for Caprini scores between 1 and 10; estimates beyond a score of 10 were unstable. Receipt of pharmacologic prophylaxis resulted in a modest decrease in venous thromboembolism risk (odds ratio, 0.85; 95% confidence interval, 0.72-0.99; P = .04). However, the low overall incidence of venous thromboembolism led to large estimates of numbers needed to treat to prevent a single venous thromboembolism event. A Caprini cut-point demonstrating clear benefit of prophylaxis was not detected.

Although a linear association between the Caprini risk assessment model and the risk of venous thromboembolism was noted, an extremely low incidence of venous thromboembolism events in non-intensive care unit medical patients was observed. The Caprini risk assessment model was unable to identify a subset of medical patients who benefit from pharmacologic prophylaxis.